Hypokalemia in Emergency Medicine

Updated: Oct 10, 2022
  • Author: David Garth, MD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Practice Essentials

Hypokalemia is defined as a potassium level of less than 3.5 mEq/L, while moderate hypokalemia is a serum level of 2.5-3 mEq/L. Severe hypokalemia is defined as a level of less than 2.5 mEq/L.

Potassium is one of the body's major ions. Nearly 98% of the body's potassium is intracellular. The ratio of intracellular to extracellular potassium is important in determining the cellular membrane potential. Small changes in the extracellular potassium level can have profound effects on the function of the cardiovascular and neuromuscular systems. [1, 2, 3]

The kidney determines potassium homeostasis, and excess potassium is excreted in the urine.

The reference range for serum potassium level is 3.5-5 mEq/L, with total body potassium stores of approximately 50 mEq/kg (ie, approximately 3500 mEq in a 70-kg person).

Signs and symptoms of hypokalemia

Findings that are consistent with severe hypokalemia may include the following:

  • Signs of ileus
  • Hypotension
  • Ventricular arrhythmias [4]
  • Cardiac arrest
  • Bradycardia or tachycardia
  • Premature atrial or ventricular beats
  • Hypoventilation, respiratory distress
  • Respiratory failure
  • Lethargy or other mental status changes
  • Decreased muscle strength, fasciculations, or tetany
  • Decreased or absent tendon reflexes
  • Cushingoid appearance (eg, edema)

Workup in hypokalemia

Laboratory studies in the workup of hypokalemia include the following:

  • Serum potassium level [5]
  • Blood urea nitrogen (BUN) and creatinine level
  • Glucose, calcium, and/or phosphorus level if coexistent electrolyte disturbances are suspected
  • Consider digoxin level if the patient is on a digitalis preparation; hypokalemia can potentiate digitalis-induced arrhythmias
  • Consider arterial blood gas (ABG); alkalosis can cause potassium to shift from extracellular to intracellular

Electrocardiography can reveal the following

  • T-wave flattening or inverted T waves
  • Prominent U wave that appears as QT prolongation
  • ST-segment depression
  • Ventricular arrhythmias (eg, premature ventricular contractions [PVCs], torsade de pointes, ventricular fibrillation) [4]
  • Atrial arrhythmias (eg, premature atrial contractions [PACs], atrial fibrillation)

Thyroid screening studies include assessment of thyroid-stimulating hormone (TSH), free triiodothyronine (T3), and free thyroxine (T4) in patients with tachycardia, especially Asian patients [6]


Emergency department management of hypokalemia includes the following:

  • Patients in whom severe hypokalemia is suspected should be placed on a cardiac monitor; establish intravenous access and assess respiratory status
  • Direct potassium replacement therapy by the symptomatology and the potassium level; begin therapy after laboratory confirmation of the diagnosis
  • If patients who have mild or moderate hypokalemia (potassium level of 2.5-3.5 mEq/L) have only minor symptoms, they may need only oral potassium replacement therapy; patients with mild hypokalemia whose underlying cause of hypokalemia can be corrected may not need any potassium replacement; if cardiac arrhythmias or significant symptoms are present, then more aggressive therapy is warranted
  • If the potassium level is less than 2.5 mEq/L, intravenous potassium should be given
  • The serum potassium level is difficult to replenish if the serum magnesium level is also low; look to replace both


Hypokalemia may result from conditions as varied as renal or GI losses, inadequate diet, transcellular shift (movement of potassium from serum into cells), and medications.




United States

In a study of about 47,000 emergency department visits in which adult patients underwent potassium measurements, Singer et al found that 1 in 11 patients had hyperkalemia or hypokalemia, with the potassium level being below 3.5 mEq/L in 5.5% of individuals. [7]

As many as 20% of hospitalized patients are hypokalemic; however, hypokalemia is clinically significant in only about 4-5% of these patients. Severe hypokalemia is relatively uncommon.

Up to 14% of outpatients who undergo laboratory testing are found to be mildly hypokalemic.

Approximately 80% of patients who are receiving diuretics become hypokalemic.


In an Italian study, Giordano et al found that of 7941 emergency department patients, 13.7% of them had an electrolyte imbalance, with hyponatremia being the most common (44%) and hypokalemia being the next most frequent (39%). The investigators also found that 98% of patients with an electrolyte imbalance had an associated systemic disease. [8]

A retrospective, single-center Japanese study by Makinouchi et al found the prevalence of severe hypokalemia (defined in the report as a serum potassium level of 2.5 mEq/L or less) in the emergency department to be 0.4%. The report was restricted to adult patients. [9]


Incidence is equal in males and females.



Hypokalemia usually resolves with appropriate therapy. However, in the aforementioned study by Singer et al of adult emergency department patients, hyperkalemia and hypokalemia were implicated as risk factors for death, relative to their severity. [7]

Similarly, a study by Krogager et al indicated that patients with hypertension who have a potassium level outside of the 4.1-4.7 mmol/L range, including those who are hypokalemic or hyperkalemic, have an increased mortality risk. For patients with hypokalemia, the 90-day mortality rate was 4.5%, compared with 1.5% for the 4.1-4.7 mmol/L range. [10]

A study by Kieneker et al indicated that not only is hypokalemia linked to the progression of existing chronic kidney disease (CKD), it is also associated with an increased risk of developing CKD, either with or without diuretic use. [11]

A retrospective study by Marill and Miller of emergency department patients indicated that hypokalemia is strongly associated with prolonged heart rate–corrected QT (QTc) duration, particularly in women. The study found that in patients with a potassium level below 3.9 mmol/L, every 1 mmol/L reduction in potassium increased the QTc time by 43.0 ms in women and 29.5 ms in men. [12]


Patient Education

Diet modification is recommended for those patients who are predisposed to hypokalemia. Increase intake of bananas, tomatoes, oranges, and peaches because they are high in potassium.

For patient education resources, see the Endocrine System Center, as well as Low Potassium.